Identifying diseases that might be associated with environmental contaminants, and determining the existing data sources available for them, [ is a key part of the effort to better characterize links between environmental exposures and adverse health outcomes.
Tracking overall rates of disease in the nation, independent of exposure, enables the evaluation of disease patterns and emerging

trends. It may identify diseases, conditions, and possible risk factors that warrant further study or intervention and can help identify where policies or interventions have been successful. Because the U.S. has a diverse population, an important component of such an analysis is identifying disparities among people of differing races and ethnicities, genders, education and income levels, and geographic locations. ................ ]

Weegy: Aging of population (also known as demographic aging, and population aging) is a summary term for shifts in the age distribution (i.e., age structure) of a population toward older ages. [ A direct consequence of the ongoing global fertility transition (decline) and of mortality decline at older ages, population aging is expected to be among the most prominent global demographic trends of the 21st century. Population aging is progressing rapidly in many industrialized countries, but those developing countries whose fertility declines began relatively early also are experiencing rapid increases in their proportion of elderly people. This pattern is expected to continue over the next few decades, eventually affecting the entire world. Population aging has many important socio-economic and health consequences, including the increase in the old-age dependency ratio. It presents challenges for public health (concerns over possible bankruptcy of Medicare and related programs) as well as for economic development (shrinking and aging of labor force, possible bankruptcy of social security systems). ..................Defining and measuring population aging
As the study of population aging is often driven by a concern over its burdening of retirement systems, the aging of population is often measured by increases in the percentage of elderly people of retirement ages. The definition of retirement ages may vary but a typical cutoff is 65 years, and nowadays a society is considered relatively old when the fraction of the population aged 65 and over exceeds 8-10%. By this standard, the percentage of elderly people in the United States stood at 12.6% in 2000, compared with only 4.1% in 1900 and a projected increase to 20% by the year 2030.
A related measure of population aging is the elderly dependency ratio (EDR): the number of individuals of retirement ages compared to the number of those of working ages. ] (More)